The objectives are (a) to determine how the neurotrophin, nerve growth factor (NGF), acts on specific populations of nerve cells to mediate their survival and differentiation in development, and regeneration after injury or age-related damage and (b) to identify genes in non-neuronal cells of peripheral nerve that play roles in nerve degeneration and successful regeneration. Both objectives have immediate relevance to clinical problems of widespread occurrence, namely the neurodegenerative diseases and the chronic or acute injuries to neurons in the CNS and PNS. The approach will be to determine whether and how the two NGF receptors and/or their signal transduction mechanisms interact in the mechanism of action of NGF by comparing the binding and kinetic properties of the receptors for NGF and mutant NGFs, expressed alone or in combination, in different types of cells and the genes that these receptor interactions activate. The specificity of the action of NGF will be explored by comparing this data with that obtained with the neurotrophin NT-3 which also binds to these two NGF receptors. Whether or not the cytoplasmic domain of the low affinity NGF receptor can induce a signal transduction mechanism by itself or in appropriate chimeric receptor will also be tested and the nature of this signal, particularly its putative action through G proteins, examined. The developmental expression of the two receptors in the well-defined trigeminal ganglion system of the mouse will be compared to determine the onset of sensory neuron NGF dependency. The ability to obtain correct folding and processing of NGF and BDNF (brain-derived neurotrophic factor) and the regulation of their secretion will be examined by the transient expression of deletion and other mutants of their corresponding precursor proteins. Further studies of the myelin protein encoded by one of the genes repressed after nerve injury will be aimed at confirming its location in the myelin sheath, identifying its genomic structure and the regulatory elements in the promoter region of the gene and, by expression in Schwannoma or primary Schwann cell cultures, determining if the protein or its mRNA control the proliferation of these cells after nerve injury, as indicated by its homology to a growth arrest specific protein. The chromosomal location of the gene in man will be determined and its possible involvement in one of the major inherited human motor and sensory neuropathies explored. These studies are the paradigm for the examination of the other novel sequences regulated after nerve injury.